Acoustical titanium diaphragm and method for heat treating same



- .Max-ch 24, 1959 Tosi-11o HAYAsAKA l-:TAL 2,879,193

ACOUSTICAL TITANIUM DIAPHRAGM AND METHOD v FOR HEAT TREATING SAME FiledMay 3, 1956 2 sheets-sheet 1 .SHozo NA GA l THE/E A Trae/v5 Y March 24,1959 TosHlo HAYAsAKA ET AL AcousTIcAL TITANIUM DIAPHRAGM AND METHOD FORHEAT TREATING SAME Flled May 5, 1956 2 Sheets-Sheet 2 WORKING P/NT A IR6A P (M/L/Mfrms) /Nvsu roes TosH/o HA YA sA KA Keb/Ro MAsdZAwA .SA/alzoNAGA/ 5);@ 'mg/Ma THE/g A rromvsv Unitey States Patent O 2,879,193ACoUs-TICAL TrrAN'IUM DIAPHRAGM AND MErHoD Fon HEAT TREATING SAME ToshioHayasaka, Kenro Masuzawa, and vShozol Nagai,

Tokyo, Japan, assignors to Nippon Telegraph & Telephone PublicCorporation, Tokyo, Japan, a corporation of Japan Application May 3,1956, Serial No. 582,598

Claims priority, application Japan May 11, 1955 7 Claims. (Cl. 14S-21.9)

This invention relates to a diaphragm for acoustic apparatus, and moreparticularly to a diaphragm made of titanium.

It is well known that duralumin is generally used as material foracoustic diaphragm. Compared with duralumin, titanium has substantiallythe same strength/ density; however, it has a stronger resistanceagainst corrosion; its drawability and formability are superior to thoseof duralumin; and its coeflicient of thermal expansion is smaller.Therefore, the diaphragm made of titanium is considered excellent foracoustic apparatus of high quality, for example, standard apparatus foracoustic measurement. It must be noted, however, that, in case adiaphragm which is always under stress, such as a diaphragm fortelephone receivers and a diaphragm for condenser microphones, is madeof titanium, the efciency of the apparatus varies gradually, due todeformation thereof caused by creep phenomenon of titanium, andtherefore, the stability of eiiiciency cannot be expected.

The object of the present invention is to provide a titanium diaphragmfor acoustic apparatus in which the efliciency is substantiallyinvariable.

In order to accomplish the above object, the feature of the presentinvention is to make a diaphragm by forming a titanium sheet in adesired form, and thereafter applying heat treatment thereto, or to makea diaphragm by applying heat treatment to a titanium sheet at the statewhere tension is applied.

The results of the experiments made by the inventors revealed that atitanium diaphragm obtained by forced aging, which constitutes thecharacteristic of the invention, produces almost no diaphragmdeformation to be caused by creep phenomenon, in case such diaphragm isused for telephone receivers or condenser microphones.

In the attached drawings,

Fig. 1 shows the variation of resonance frequency of a diaphragm forcondenser microphones, by taking the lapse of time as abscissa.

Fig. 2 shows the pull which works to a diaphragm for telephonereceivers, as function of air gap length.

Fig. 3 shows the deformation of a diaphragm for telephone receivers asfunction of the lapse of time, in case a load of 1,000 gr. w. is appliedthereto.

To a diaphragm for condenser microphones, a stress of about 15 kg./mm.2is always working. Therefore, the diaphragm is gradually elongated andthe stress working thereupon is decreased whereby the resonancefrequency is lowered down, and as the result thereof, the efficiency ofthe microphone gradually increases. The resonance frequency of thediaphragm, which is formed with a titanium sheet, without forced aging,is lowered down, as shown by the curve I in Fig. 1, as time elapses. Inview of the characteristic of the curve I, it is supposed that about oneyears time is required for the diaphragm to stabilize, by ceasing todeform, and to be practically used. On the other hand, the variation ofresonance frequency of a diaphragm to which heat treatment has been r.ICC..

applied for 6 hours atfthe temperature -of1200 inthe air, at the statewhere tension is worked-after the formaonance frequency is abruptlylowered down as Ishown by,

the dotted line B. However, after the-heat treatment, the

resonance frequency of the diaphragm is remarkably sta;

bilized as shown by the curve d-e. The valueof thev resonance frequencyshown by the part d-e in the curve II is supposed to be almostequivalent to that of the resonance frequency, to be arrived at by adiaphragm, to which no heat treatment is made, after having been left tostand for decades.

It must be noted that, in a diaphragm for condenser microphones, nostabilized resonance frequency, as shown by the curve II in Fig. 1, canbe attained, if tension is applied thereto after heat treatment.

To a diaphragm for telephone receivers, a pulling force is alwaysworking by permanent magnet. This pulling force is the function of airgap as shown in Fig. 2, which is about 300 gr. w. at working gap, andabout 1000 gr. w. at zero gap. Therefore, the diaphragm for telephonereceivers is deformed by the creep phenomenon due to the above pullingforce, air gap is decreased, and the efficiency of the receiver islowered down.

When a load of 1000 gr. w. is applied to a diaphragm formed of titaniumsheet without forced aging, the deformation is produced, as timeelapses, as shown by the curve I in Fig. 3. On the other hand, thedeformation produced by applying a load of 1000 gr. wl to a diaphragmformed of titanium sheet, to which heat treatment is made for 10 hoursat the temperature of 200 C., is shown by the curve Il in Fig. 3. Asshown in Fig. 3, the deformation of the diaphragm to which heattreatment is applied does not exceed 3 microns, and the deformationspeed after hours is very small. Therefore, the eiciency of thetelephone receivers in which a heat-treated diaphragm is used scarcelyvaries by use. The higher the temperature for heat treatment is, theshorter the time required for heat treatment is. However, since titaniumbegins to recrystallize and oxidate at the temperature of about 400 C.,it is necessary to make the temperature for heat treatment as under 400C. The temperature at which the strain aging occurs is near to the roomtemperature. However, it takes much time before the effect of heattreatment is produced, if a temperature below 100 C. is used, and thisis improper for actual practice. It is, therefore, desirable to have theheat treatment temperature within the sphere of 100 C.- 400 C.

We claim:

1. A titanium diaphragm for acoustic apparatus, characterized by adiaphragm formed from a titanium sheet and having a relatively lowstabilized resonant frequency abruptly changed from a relatively highresonant frequency by a heat treatment applied thereto at a temperatureof approximately 200 C., which is above the starting temperature ofstrain aging of titanium and below the starting temperature of therecrystallization of titanium.

2. A diaphragm as in claim 1, in which the low stabilized resonantfrequency was abruptly affected by a heat treatment made for more thanone hour.

3. The method of producing a frequency stable titanium diaphragm foracoustic apparatus comprising the steps of forming the diaphragm from atitanium sheet providing a relatively high resonant frequencycharacteristic in the diaphragm, heating this formed diaphragm to atemperature above the starting temperature of strain aging of titaniumand below the starting temperature of the recrystallization of titaniumto abruptly lower and stabilize the resonant frequency of the formeddiaphragm.

i4.- The method of producing the diaphragm of claim 3 References Citedin the tile of this patent characterized in that the step of heating isapplied for a UNITED STATES PATENTS period of more than one hour. 1 204096 N 5. The method of producing the diaphragm of claim 3 Waller ov 71915 characterized in that the vstepof heating is carried o'n 5 OTHERREFERENCES between 'the temperatures of 100 C. and 400 C. Tt d t th 6;The method of producing the diaphragm of claim 3 lgsalgull. I s AlloysMatenals and Me ods' May characterized in that the step of heating iscarried on a temperature of approximately 200 C. 9'5 1 33 7. The' methodof producing the diaphragm of claim 6 10 1 3 pages 3? 3 characterized inthat the step of heating is applied for a period of ten hours.

Kiessel et al.: Iournalof Metals, v. 5, sec. 2v, February

1. THE METHOD OF PRODUCING A FREQUENCY STABLE TITANIUM DIAPHRAGM FORACOUSTIC APPARATUS COMPRISING THE STEPS OF FORMING THE DIAPHRAGM FROM ATITANIUM SHEET PROVIDING A RELATIVELY HIGH RESONANT FREQUENCYCHARACTERISTIC IN THE DIAPHRAGM, HEATING THIS FORMED DIAPHRAGM TO ATEMPERATURE ABOVE THE STARTING TEMPERATURE OF STRAIN AGING OF TITANIUMAND BELOW THE STARTING TEMPERATURE OF THE RECRYSTALLIZATION OF TITANIUMTO ABRUPTLY LOWER AND STABILIZE THE RESONANT FREQUENCY OF THE FORMEDDIAPHRAGM.